Rail police were flapping when they found small pebbles
and gravel on stretches of North-east railway sleepers.

But you could have knocked them down with a feather when
they discovered the bird-brained culprits were crows!

Sgt Mike Burnett of British Transport Police said: "The
problem was spotted by an engineer doing maintenance work.

"It was first reported as people putting stones on the
line.

"But something did not make sense. It was out at Kennethmont
and Huntly and that's not an area where we would expect trouble.

"Our first thought was kids, but it's in the middle of
nowhere."

Then an eagle-eyed signal operator solved the mystery.

Mike said: "He spotted the birds putting them on the lines
so the trains would go over them."

It turns out the crows know exactly what they're doing.

They place the stones on the tracks, wait for trains to
run over them, then swallow the debris, which helps them digest their food.

At first Mike thought it was a wind-up.

"I checked the date to see it wasn't April 1.

"I've been in this job for 20 years and never known anything
like it."

It was also news to Julia Harris, of the Royal Society
for the Protection of Birds.

She said: "I've never heard of that before, but crows
are definitely known as being among the most inventive birds, like others from the same family such as jackdaws."

She says crows and other birds have no teeth so they need
to swallow grit to help them grind up their food.

A ScotRail spokesman said: "I think that's absolutely
amazing. It sounds like something out of Alfred Hitchcock's The Birds."

But he didn't think the rail company would be taking any
measures to clip the culprits' wings.

He said: "We have enough problems already with people
putting washing machines and allsorts on railway lines.

"At least these birds are doing something for a proper
purpose. This is a serious part of their life," he said.

The tale of the brainy birds coincides with a major conference
in Aberdeen
today.

The 8th International Seabird Group Conference, being
held in the city today and tomorrow, was being told that Aberdeen
is believed to have the world's biggest population of roof-nesting herring gulls.

It had been hoped that Aberdeen's refuse switch from black bags to wheelie bins would put an end to the gull menace.

But the large birds, with the characteristic blood-red
mark on their beaks, have not been completely run out of town.